attention contact printers! when i put a negative in my printing frame and lock the back, there are Newton rings between the glass and the negative. lots of the m. lots of colorful little asymmetrical little designs. does anyone know what is causing this? i've cleaned the glass, first with glass cleaners and then with s oap and water; the rings are still there. i've put negatives which i've processe d at different times in, and the rings are still there. i've never seen these ri gns in my prints before; now they appear in my prints. does anyone have any sugg estions?